CDIA Image Processing 4 — Questions and Answers
Question 1: When scanning documents at 200 DPI versus 300 DPI, what is the primary trade-off?
- 200 DPI produces larger files but better OCR accuracy
- 300 DPI produces smaller files but lower quality
- 200 DPI has smaller files but may reduce OCR accuracy for small fonts (Correct answer)
- 300 DPI is required for color scanning only
Correct answer: 200 DPI has smaller files but may reduce OCR accuracy for small fonts
Lower DPI (200) produces smaller file sizes but may reduce OCR accuracy, especially for small or complex fonts that need more pixel detail.
Question 2: What is 'line removal' preprocessing used for in document imaging workflows?
- Eliminating horizontal and vertical lines (e.g., table borders, form lines) before OCR to improve character recognition (Correct answer)
- Removing colored lines from grayscale conversions
- Detecting line breaks between paragraphs
- Straightening diagonal text lines
Correct answer: Eliminating horizontal and vertical lines (e.g., table borders, form lines) before OCR to improve character recognition
Line removal extracts horizontal and vertical ruling lines from forms or tables before OCR, preventing lines from being misread as characters.
Question 3: Which image quality attribute is most directly affected by the bit depth of a scanner?
- Spatial resolution
- Tonal range and color accuracy (Correct answer)
- Scanning speed
- Document feed capacity
Correct answer: Tonal range and color accuracy
Bit depth determines how many distinct tonal values or colors can be captured, directly affecting the tonal range and color accuracy of the scanned image.
Question 4: In document imaging, what does 'punch hole removal' accomplish?
- Deletes binder holes from scanned pages by filling them with background color (Correct answer)
- Removes staple marks from document corners
- Eliminates binding shadows from book scans
- Crops pages to standard letter size
Correct answer: Deletes binder holes from scanned pages by filling them with background color
Punch hole removal detects circular holes along document edges (from 3-hole punches) and fills them with the background color to prevent OCR errors.
Question 5: What is the purpose of gamma correction in scanned document images?
- Adjusting the nonlinear relationship between pixel values and actual brightness for accurate display (Correct answer)
- Converting color documents to grayscale
- Increasing the DPI of a scanned image
- Applying compression to reduce file size
Correct answer: Adjusting the nonlinear relationship between pixel values and actual brightness for accurate display
Gamma correction compensates for the nonlinear response of displays and scanners, ensuring that perceived brightness matches the intended tonal values.
Question 6: Which technique is used to detect and correct for the curvature of text lines in book scanning?
- Deskew
- Dewarping (Correct answer)
- Binarization
- Descreening
Correct answer: Dewarping
Dewarping corrects the 3D distortion and curved text lines that result from book page curvature near the binding during flatbed scanning.
Question 7: What does the term 'lossless compression ratio' mean in the context of document image compression?
- The ratio of the original file size to the compressed file size with no image data lost (Correct answer)
- The percentage of image quality degraded after compression
- The number of compression passes applied to an image
- The ratio of color to grayscale pixels in a document
Correct answer: The ratio of the original file size to the compressed file size with no image data lost
Lossless compression ratio is the factor by which file size is reduced without discarding any image data, so decompression perfectly reconstructs the original.
CDIA Image Processing 4
When scanning documents at 200 DPI versus 300 DPI, what is the primary trade-off?